/Engine/Source/Runtime/Slate/Public/Widgets/Input/SEditableText.h
Compute the Geometry of all the children and add populate the ArrangedChildren list with their values. Each type of Layout panel should arrange children based on desired behavior.
virtual void OnArrangeChildren ( const [FGeometry](API\Runtime\SlateCore\Layout\FGeometry) & AllottedGeometry, [FArrangedChildren](API\Runtime\SlateCore\Layout\FArrangedChildren) & ArrangedChildren ) const